TThreadList access violation on locklist

Question

var   all: TThreadList = nil;

procedure TForm1.IdTCPServer1Connect(AContext: TIdContext);
var  list:tlist;
begin
  try
  list := all.LockList;
  try
    list.Add(0);
  finally
    all.UnlockList;
  end;
  except

  end;
end;

telnet 127.0.0.1 1234

why it's getting access violation ?

score 8 · Answer 1 · answered Nov 26 '12 at 23:08

8

I expect you simply forgot to create the TThreadList. You need

all := TThreadList.Create;

somewhere. For example, in the initialization section of that unit.

answered Nov 26 '12 at 23:08

David Heffernan

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Whenever you get an access violation on a method call, check whether or not the instance variable is valid. In the debugger, you will see that `all` evaluates to `nil`. That's your tell tale sign. – David Heffernan Nov 26 '12 at 23:11
Local POD-type variables, like raw pointers, are not initialized to zero/nil. So no, it is not guaranteed that the debugger would show `nil` for the `all` variable. – Remy Lebeau Nov 26 '12 at 23:49
@Remy, in this case yes, since OP has it initialized to `nil`. – TLama Nov 27 '12 at 00:06
@TLama: sorry, my bad. I read the code wrong, I didn't notice `all` was a global variable. – Remy Lebeau Nov 27 '12 at 00:21
@waza123 Is this the answer to your question? – David Heffernan Nov 27 '12 at 17:46

TThreadList access violation on locklist

1 Answers1